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Tuesday, July 15, 2014

In the Packaging chapter of American Sour Beers I included formulas designed to estimate the amount of carbonation that will be produced by the microbes when blending similar sour beers of different gravities. While I believe it is important to understand the logic behind the math, it is certainly much easier to simply plug in the numbers rather than solve equations by hand. A few weeks ago someone emailed a question about the formulas, which sparked me to put together an easier method. I finally found time to refine it, so here I present my Blending Priming Calculator spreadsheet! Unlike the formulas in the book, it can determine carbonation for a blend of up to five beers.

These formulas are only exact if the wort for each component is identical. Having the same carbohydrate profile ensures that the remaining dextrins in one batch would be fermentable by the bacteria and Brettanomyces present in another. You’d expect the final gravity of the blend to approach the final gravity of the driest component, which is why this component must be entered in a specific position in the spreadsheet. Even then there is no way to guarantee the accuracy of the calculation because more attenuative microbes could be "hiding" in a younger/sweeter component.

To use the spreadsheet, start by selecting the number of component beers you will be blending from the drop-down list. This selection controls which formulas are used from the hidden Calculations tab.

Input the peak temperature the beer reached after the gravity stabilized (this is the same as all other priming calculators). If you ferment a
beer through a warm summer and it continues to ferment into the fall, but stops before winter, you’d note the temperature it was when you stopped seeing the gravity drop (assuming it didn't get warmer after that). If the beer fermented all winter, but aged into the hot summer, you'd note the hottest temperature it reached during the summer.

I’ve noticed anecdotally that long-term aging in a barrel knocks about half of the assumed residual carbonation out of the beer. The "Residual CO2 Volumes" in red will calculate automatically. If you happen to own a capable CO2 meter (aren't you lucky!), you could override these calculation and simply enter the measured volumes of CO2 in row 5.

At this point enter the current gravity reading for each component and the volumes of beer that you plan to include in the blend. With those pieces of information entered you can see how much residual carbonation the blend will contain at bottling, and after it completes bottle-fermentation (assuming no priming sugar).

Input the target volumes of CO2 desired, and the formulas will display how
much table or corn sugar would be required to carbonate the beer to that level. As we
are assuming the fermentation of dextrins from the blended beers, it may take 6-12 months
of cellaring to achieve full carbonation (as is carried out by traditional Belgian gueuze
blenders).

I’ll certainly update this spreadsheet as I think of improvements (and hear your suggestions). At a minimum I'll add a metric tab as the metric formulas are already presented in the book.

It won't do that calculation automatically, but you could certainly just play with the amounts of the old and young beer until the number in "anticipated CO2 - without sugar" matched your target. Best of luck!

You can use the solver in Excel to figure out what blend ratio to use to arrive at a specific value for Anticipated CO2 - Without Sugar. Say you plan to blend together one new lambic with one old lambic. You would set the parameters of each in slots 1 and 2 of the spreadsheet, set the volume you plan to use for one of them, then use the solver to give you the volume you need of the other one to get the desired volumes of CO2. To do this you open the solver, use cell H11 in the "Set Objective" field, use cell B2 or C2 in the "By Changing Variable Cells" field (depending on which volume is your unknown), then click solve and it should find you your answer. Hope this helps!

Mike, this is somewhat related but in your book (p. 97) you mention Jolly Pumpkin keg conditions their beer. Does this mean their beers do not see brite tanks? Do they keg primed, uncarbonated beer and allow a few weeks at warm temps to carbonate?Some further insight would be awesome, cheers!

Thanks Greg, one of the great things about writing this blog is how much I get to learn!

Best of luck with things at Council Brewing Jeff! If you have any suggestions or improvements, let me know!

Jonathan, I don't have any more specifics on Jolly Pumpkin's kegging process. They may keg completely flat beer with priming sugar, or they may partially force carbonate and then lightly prime. Either way likely the beer spends at least a little time in a brite or blending tank.

Why not bulk prime with a sugar solution? Adding dry sugar can cause the beer to foam and lose some of its residual carbonation. Do you have a scale accurate enough to measure tenths of a gram (or at least grams)?

Have you had stable gravity readings month-over-month? Even a beer at 1.005 could drop enough to cause over-carbonation if it isn't finished.

There's no way to estimate how much sugar to add without knowing how much carbonation you want the beer to have. Same goes for how long it'll take, without knowing anything else about the beer.

Hey Mike, Your observation of CO2 reduction in barrel aged beers seem counterintuitive to me. Although at times, my brain is not very intuitive. Assuming that the beer is barrel aged at a temperature lower than fermentation temperature, it would seem that over time the beer would actually pick up more CO2 or whatever gas was available to it. While I have yet to barrel age a beer, I am trying to learn as much as possible before making such a long term commitment. I do brew a lot of Brett secondaried beers and part of my process includes an extended cold crash (~3 weeks) to reduce the Brettanomyces population to very low numbers (I believe a low population of Brett in the bottle does wonderful things). Knowing that cold beer holds more gas that warm beer and worrying that the beer would take on oxygen during the long cold period, I attach a nitrile glove to the neck of the carboy and inflate with CO2. During the first 72 hours of the crash, the glove has to be re-inflated 2 or 3 times, indicating the the beer is taking on CO2. The first time I did this, I allowed the beer to come back to 60F for bottling as I like to pitch Sacc at bottling. As the temperature increased the glove re-inflated and much of the dropped yeast went back into suspension, indicating the CO2 gassing off. Since then I transfer to a CO2 purged and sealed bottling vessel prior to warming. Sorry for the long statement but it is this experience that has me wondering why a barrel aged beer would decrease in CO?

SOrry for not replying previously, but you got it. The combination of nucleation and lower head pressure (thanks to gas exchange through the wood) likely combine to reduce the amount of carbonation in solution. It'll depend though, if you package while the Brett is still slowly working then there may be a more standard amount of CO2.